All-perovskite tandem solar cells achieving >29% efficiency with improved (100) orientation in wide-bandgap perovskites.

Monolithic all-perovskite tandem solar cells present a promising approach for exceeding the efficiency limit of single-junction solar cells. However, the substantial open-circuit voltage loss in the wide-bandgap perovskite subcell hinders further improvements in power-conversion efficiency. Here we develop wide-bandgap perovskite films with improved (100) crystal orientation that suppress non-radiative recombination. We show that using two-dimensional perovskite as an intermediate phase on the film surface promotes heterogeneous nucleation along the (100) three-dimensional perovskite facets during crystallization. Preferred (100) orientations can be realized by augmenting the quantity of two-dimensional phases through surface composition engineering, without the need for excessive two-dimensional ligands that otherwise impede carrier transport. We demonstrate an open-circuit voltage of 1.373 V for 1.78 eV wide-bandgap perovskite solar cells, along with a high fill factor of 84.7%. This yields an open-circuit voltage of 2.21 V and a certified power-conversion efficiency of 29.1% for all-perovskite tandem solar cells, measured under the maximum power-point conditions.